Communications between two or more humans, or between a human and a machine, is traditionally dominated by visual and verbal information and alphanumeric input. Efforts to automate human-to-human or human-to-machine communication, such as commercial speech recognition have emphasized the audible aspects. A totally auditory communication strategy places a number of constraints on the communication channels, including sensitivity to ambient noise, a requirement for proper formation and enunciation of words, and use of a shared language. The physical limitations of sound production and recognition also become problematic in unusual environments, such as those involving hazardous materials (HAZMATs), extra vehicular activity (EVA) space tasks, underwater operations and chemical/biological warfare (CBW). Conventional auditory expression may be undesirable for private communication needed in many situations encountered daily, such as discrete or confidential telephone calls, offline or sotto voce comments during a teleconference call, certain military operations, and some human-to-machine commands and queries. Communication alternatives that are both private and not dependent upon production of audible signals are valuable.
One proposed method for studying alternative means of communication is direct understanding of brain signals, which bypasses speech and its analysis altogether. J. R. Wolpaw et al, “Brain-computer interface technology: a review of the first international meeting,” I.E.E.E. Trans. on Rehabilitation Engineering, vol. 8 (2000) 164-171, recently published a review of the state of electroencephalograph (EEG) analysis. Several practical difficulties are encountered for near term application of pure EEG approaches, due to use in EEG of aggregated surface measured brain potential. Additionally, one confronts the nonlinear complexity and idiosyncratic nature of the signals. An alternative, invasive EEG measurement and analysis, is not considered practical for widespread use, except for extreme medical conditions.
What is needed is a sub-audible communication system that provides one or more tiers, in addition to conventional audible communication, to exchange or transfer information compactly, reliably and reasonably accurately. Preferably, the amount of computation required should be modest and not be out of proportion to the information obtained through the signal processing.